Trace elements in lake sediments measured by the PIXE technique

Lakes are ecosystems where there is a great potential of metal accumulation in sediments due to their depositional characteristics. Total concentratio n of trace elements was measured on a 50 cm long sediment core from the Inf ernao Lake, that is an oxbow lake of the Moji-Guacu River basin, in the sta te of Sao Paulo, Brazil. Dating of the core shows up to 180 yrs old sedimen t layers. The use of the PIXE technique for elemental analysis avoids the t raditional acid digestion procedure common in other techniques. The multiel emental characteristic of PINE allows a simultaneous determination of about 20 elements in the sediment samples, such as, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Zr, Ba, and Pb. Average values for the elemental composition were found to be similar to the bulk crustal composit ion. The lake flooding pattern strongly influences the time series of the e lemental profiles. Factor analysis of the elemental variability shows five factors. Two of the factors represent the mineralogical matrix, and others represent the organic component, a factor with lead, and another loaded wit h chromium, The mineralogical component consists of elements such as, Fe, A l, V, Ti, Mn, Ni, K, Zr, Sr, Cu and Zn. The variability of Si is explained by two distinct factors, because it is influenced by two different sources, aluminum-silicates and quartz, and the effect of inundation are different for each other. The organic matter is strongly associated with calcium, and also bounded with S, Zn, Cu and P. Lead and chromium appears as separated factors, although it is not clear the evidences for their anthropogenic ori gin. The techniques developed for sample preparation and PIXE analysis was proven as advantageous and provided very good reproducibility and accuracy. (C) 1999 Elsevier Science B.V. All rights reserved.